An accidental ultrasonic noise source in the mouse facility activating a band of neurons in the inferior colliculus.

Experimental animals are housed under tightly regulated conditions to standardize experiments and minimize the number of animals per experiment. Ultrasonic noise pollution is a potential problem in housing as it is inaudible for humans, and may thus remain undetected, whereas most laboratory animals can hear ultrasound. Compared with sounds audible to humans, ultrasonic noise has received much less attention, yet it can likewise induce physiological and behavioral effects in animals, including deleterious effects on welfare and on experimental reproducibility. In this study, we accidentally discovered that our mouse stable was polluted by an ultrasonic beep emitted by a radio. To investigate the impact of this beep, we tested under which conditions this beep would activate neurons in the inferior colliculus (IC) using the c-fos promotor in TRAP2 mice as a marker for activation. Exposure to the beep of the radio activated a band of neurons. A similar band was observed in the TRAP2 mice following exposure to a beep with the same frequency as the radio beep, and the location of the bands in both cases agreed with the tonotopic organization of the IC. A similar ultrasonic tone was observed in more than half of commercially available radios, indicating that the presence of a radio is likely to expose animals to a continuous tone that is inaudible to humans. Based on our findings, we therefore recommend that animal facilities routinely check for ultrasonic noise contamination to increase animal welfare and enhance study reproducibility.